1.

For any sets A, B and C prove that:A × (B ∪ C) = (A × B) ∪ (A × C)

Answer»

Given:

A, B and C three sets are given. 

Need to prove: A × (B ∪ C) = (A × B) ∪ (A × C) 

Let us consider, (x, y)A × (B ∪ C) 

⇒ x∈A and y∈(B ∪ C)

⇒ x∈A and (y∈B or y∈C) 

⇒ (x∈A and y∈B) or (x∈A and y∈C) 

⇒ (x, y)∈(A × B) or (x, y)∈(A × C) 

⇒ (x, y)∈(A × B) ∪ (A × C)

From this we can conclude that, 

⇒ A × (B ∪ C) ⊆ (A × B) ∪ (A × C) ---- (1) 

Let us consider again, (a, b)∈(A × B) ∪ (A × C) 

⇒ (a, b)∈(A × B) or (a, b)∈(A × C) 

⇒ (a∈A and b∈B) or (a∈A and b∈C) 

⇒ a∈A and (b∈B or b∈C) 

⇒ a∈A and b∈(B ∪ C) 

⇒ (a, b) ∈A × (B ∪ C)

From this, we can conclude that, 

⇒ (A × B) ∪ (A × C) ⊆ A × (B ∪ C) ---- (2)

Now by the definition of the set we can say that, from (1) and (2), 

A × (B ∪ C) = (A × B) ∪ (A × C) [Proved]



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